1. Field of the Invention
The invention relates to an open-end spinning unit. More specifically, it relates to an improvement in the conveyance of fiber by a rotor-type open-end spinning unit from the fiber supply duct thereof to a fiber-collecting groove thereof.
2. Description of the Prior Art
The drawbacks of the prior art are explained below with reference to FIGS. 1 to 4.
In the conventional rotor-type open-end spinning unit shown in FIG. 1, a sliver 3 supplied through an inlet 2 of the unit 1 is guided to a combing roller 6 by a feed roller 4 and a presser 5, by which the sliver 3 is pressed onto the feed roller 4. Then the sliver 3 is opened into individual fibers by the combing roller 6, and, at the same time, foreign matter 7 such as leaves and trash are expelled through an outlet 8. Thereafter, the opened fibers are transported to a spinning chamber 10 of a rotor 9 through a fiber supply duct 11 by an airstream created by a subatmospheric pressure in the chamber 10. The fibers thus transported into the chamber 10 reach an inner wall 9a of the rotor 9 and are maintained thereon by a centrifugal force imparted thereby by the rotor 9. Then the fibers slide toward a fiber-collecting groove 13, in which the fibers are collected in the shape of a ribbon. The fiber ribbon is drawn out, through a yarn guide hole 14, of the chamber 10 while it rotates and thereby is twisted to form a yarn.
The spinning chamber 10 is defined by an inner space of the rotor 9 in a cup-shape having the inner wall 9a and a bottom wall 9b. An open space of the rotor is substantially closed by a closing component 20 formed by part of the frame of the spinning unit 1. The component 20 projects into the rotor 9 as a frustum-shaped portion 20a on a side wall of which outlet opening 11a of the fiber supply duct 11 is provided.
There are two types of exhaustion in the spinning chamber 10 for obtaining a subatmospheric pressure therein. One type is forced exhaustion, in which the air in the chamber 10 is sucked out through a clearance between the closing component 20 and the rotor 9 by a suction means (not shown) connected to an outlet 16 on a housing 15 covering all of the rotor 9. The other type is a self-exhaustion, in which the air in the chamber 10 is expelled through a plurality of apertures (not shown) provided radially on the bottom wall 9b of the rotor 9 by a centrifugal force imparted by the rotor 9. It is desirable in both types of exhaustion that the fibers transported into the chamber 10 through the fiber supply duct 11 be immediately transferred from an airstream 12 of the duct 11 to a vortex whirling in the vicinity of the inner wall 9a so that they can reach the inner wall 9a as soon as possible. In the conventional spinning unit, however, some of the fibers often fail to smoothly reach the vortex. Such fibers float in a vacant space of the spinning chamber 10 and are finally folded into a fiber bundle which is drawn out through the yarn guide hole 14, resulting in a slubby yarn. Even if the fibers reach the inner wall 9a, they tend to deposit in a disordered state in the fiber-collecting groove 13 and result in a weak yarn.
The above-mentioned problems are due to the pressure distribution and velocity distribution of the vortex in the spinning chamber 10.
According to an investigation made by the present inventors, the static pressure in the chamber 10 in the case of self-exhaustion is low near the center of the rotor 9 and sharply increases toward the inner wall 9a as shown in FIG. 2. Therefore, the fibers transported into the spinning chamber 10 from the fiber supply duct 11 tend to be sucked toward the center of the rotor 9 rather than toward inner wall 9a.
This tendency also exists in the spinning chamber 10 in the case of forced exhaustion. As is shown in FIG. 3, though the pressure distribution in the case of forced exhaustion is considerable equalized compared to that in the case of self-exhaustion, the highest pressure point is in the vicinity of the inner wall 9a.
In addition to the abovesaid pressure distribution, the vortex generated as a concomitant flow of the rotor 9 in high-speed rotation is effective only a short distance from the inner wall 9a because the velocity thereof sharply decreases as the distance from the inner wall 9a increases, as is shown in FIG. 4. Thus, the fibers transported into the spinning chamber 10 through the fiber supply duct 11 are halted midway between the opening 11a and the inner wall 9a, resulting in a plurality of floating fibers or bent fibers among the transported fibers. These floating or bent fibers cannot be restored to their original straight state even if they are subjected to the stretching action of the vortex prior to their arrival at the inner wall 9a. Therefore, the resultant yarn is both weak in strength and poor in appearance.